Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
However, tuning the
exhaust system gives lesser results in comparison with the effects of
tuning the input system (by quite a lot).

Another sweeping generalisation that is only correct 50% of the time.


But a true one. Exhaust gases are under highish pressure. Inlet merely -
at best - atomospheric. On the cylinder head and inlet manifold attention
to the inlet tract by reducing restrictions etc that shouldn't be there
but are due to the costs of removing them in manufacture, etc will pay far
more dividends than the same work carried out on the exhaust ports. And
most production cars are already fitted with free (enough) flowing
exhausts.

Not at all. Certainly in my tuning days, the SINGLE most effective way
to increase power in MOST stock engines was to hit the exhaust first.

On my old Triumph Spitfire, the gains were well known. about 10bhp
increase from a free flow exhaust, then about 7-8 from fitting bigger
carbs, and a hotter cam, and then another 5 from fitting gas flowed
head, manifold and webers rather than SU's. I went as far as a fast road
cam, better carbs, and better exhaust. Still go that car. Must get it
back on the road some day..

Similar results on BMC A series engines.

The situation was almost reversed on B series BMC engines - that engine
had a ghastly cylinder head and no amount of anything made much
difference until that was re-ported and gas flowed with better valving.

Gas flow is all about removing the major bottle necks first. If you
think exhaust is irrelevant stuff a potato in the exhaust pipe and see
how the power drops off;-)